The present invention relates to a fluid heater, or what is commonly referred to as a boiler. More particularly, the present invention relates to a fluid heater which accommodates thermal expansion and contraction.
A typical fluid heater comprises a fire tube or combustion chamber where a fuel is burned and hot combustion gases are generated, and one or more flue tubes for discharging the hot gases from the combustion chamber. An outer shell at least partially surrounding the combustion chamber and flue tubes forms a reservoir which contains a fluid, so the fluid is in contact with the external surfaces of the combustion chamber and the flue tubes. As the hot gases travel from the fire pot through the flue tubes, heat is transferred to the surrounding fluid.
Typically, flue tubes are joined at one end to the outer shell, and joined at the other end to the combustion chamber. The combustion chamber and outer shell are also joined together by other structure. This design requires the provision of a way to accommodate the thermal expansion and contraction of the flue tubes with respect to the combustion chamber and outer shell.
There are known devices which have addressed this problem. For example, expansion rings between the flue tubes and the fire pot, expansion rings between the flue tubes and the outer shell, bellows for connecting the flue tubes to the outer shell, flexible joints and a telescoping relationship between flue tubes and a gas inlet channel have been used for this purpose.